1. Filed of the Invention
The present invention relates generally to the design and use of medical devices. More particularly, the present invention relates to a method and apparatus for accessing an implanted port.
Access to a patient's vascular system can be established by a variety of temporary and permanently implanted devices. Most simply, temporary access can be provided by the direct percutaneous introduction of a needle through the patient's skin and into a blood vessel. While such a direct approach is relatively simple and suitable for applications, such as intravenous feeding, intravenous drug delivery, and other applications which continue over only a short time, they are not suitable for hemodialysis, peritoneal dialysis, hemofiltration, and other extracorporeal procedures that must be repeated periodically, often for the lifetime of the patient.
For long-term vascular access suitable for hemodialysis, hemofiltration, and the like, the most common approach is to create a subcutaneous arteriovenous (A-V) fistula. The fistula is preferably created by anastomosing an artery, usually the radial artery, to a vein, usually the cephalic vein. The vein dilates and eventually arterializes, becoming suitable for repeated puncture using a needle for access. A-V fistulas may also be created using autologous or heterologous veins, by implanting synthetic blood vessels, typically PTFE tubes, and the like.
The cannulas used for percutaneously accessing an A-V fistula may be large bore coring needles, often referred to as fistula needles. Alternatively, fistula access may be obtained using a blunt cannula which carries a removable trocar or stylet. In both cases, the cannulas are usually 15 ga. (having a bore diameter of 1.49 mm) or larger, and permit the high blood flow rates needed for hemodialysis, hemofiltration, and other extracorporeal procedures. Usually, the fistula needles or other access cannulas are introduced through a different site on the skin each time the fistula is accessed. By choosing successively different skin access sites, the tissue penetrations to the fistula are allowed to heal.
An alternative technique for repeatedly accessing an A-V fistula is referred to as the "button hole" technique. Such technique relies on repeatedly accessing the fistula through the same tissue tract, eventually creating a channel through the tissue overlying the fistula. The channel is lined with scar tissue which forms over time. While generally successful, the button hole technique results in significant back bleeding from the A-V fistula every time the fistula needle is removed after a treatment is completed. The bleeding, in turn, causes significant clot formation over the length of the tissue tract, and the resulting clot "plugs" must be removed prior to subsequent needle insertion in order to avoid the risk of pushing clot into the fistula. The removal of the clot plug causes patient discomfort and bleeding and increases the risk of infection. More significantly, should the user fail to or incompletely remove the clot plug, portions of the clot can enter circulation and cause embolism. Usually, the access tract to the A-V fistula is at a low angle over a relatively long path, increasing the discomfort, bleeding, and risks of infection and clot embolism.
While the button-hole technique for an A-V fistula can be successful when implemented by skilled personnel, and can result in decreased pain to the patient after the access channel is established, it is a very difficult procedure to learn. In particular, since the user cannot see or feel the entry point on the fistula, proper alignment of the needle to pass precisely through the established tissue tract to reach the same site on the fistula every time is very difficult. Because of the need to repeatedly pass the needle through the established tissue tract, it is recommended that the buttonhole technique be performed by the same "sticker" every time. Usually, this means that the buttonhole technique is only used by home users where the patient or a dedicated assistant can perform the needle stick each time dialysis is performed. As most dialysis is performed in clinics, however, such a requirement greatly limits the utility of the buttonhole technique.
As an alternative to the use of an A-V fistula, a variety of implantable ports have been proposed over the years for use in hemodialysis, hemofiltration, and other extracorporeal treatments. Typically, the port includes a chamber having an access region, such as a septum, where the chamber is attached to an implanted cannula which in turn is secured to a blood vessel. In the case of veins, the cannula is typically indwelling, and in the case of arteries, the cannula may be attached by conventional surgical technique.
Percutaneous access to a port through a septum, however, is generally limited to small diameter, non-coring needles. Large diameter needles will core the septum, i.e. form permanent channels therethrough, which will destroy the septum after repeated uses. Small diameter, non-coring needles will remove little or no material from the septum, allowing it to close after the needle is removed. While small needles will thus preserve the septum, they are generally incompatible with the high flow rates which are used with hemodialysis and other extracorporeal treatments.
Implantable ports having an access aperture and internal valve mechanism for isolating the implanted cannula have also been proposed. One type of implantable valved port is described in a series of issued of U.S. patents which name William Ensminger as inventor. The Ensminger access ports have internal lumens for receiving a percutaneously introduced needle and an internal valve structure for isolating the port from an associated implanted cannula. Generally, the Ensminger ports have a needle-receiving aperture which is oriented at an inclined angle relative to the patient's skin. The Ensminger ports employ relatively large funnel-like entry ports so that needles can be introduced through many different sites in accordance with conventional procedures. The Ensminger patents do not describe port access using large diameter, coring needles, such as fistula needles. Moreover, as many of the specific Ensminger designs employ elastomeric valve elements, it is likely that the valve mechanisms would be damaged if the ports were accessed by a fistula needle or other large bore coring needle. Representative Ensminger patents are listed in the Description of the Background Art below.
Thus far, implantable ports have not found wide spread acceptance in the performance hemodialysis, peritoneal dialysis, or other procedures where large volumes of blood, dialysate, or other fluids are to be exchanged. To the extent implantable ports have been used, it is generally been recommended to move the access site through the skin and/or move the skin relative to the port in order to change the location of the tissue tract between successive access procedures.
For these reasons, it would be desirable to provide improved methods and apparatus for percutaneously accessing a patient's vasculature. Such methods should reduce patient trauma, provide for reliable access to the vasculature, minimize the risk of infection to the patient, and preferably require only minor modifications to present procedures. In particular, it would be desirable to-provide methods and apparatus which combine the advantages of the "buttonhole" access technique, such as low pain needle insert and formation of a denervated tissue tract, with the advantages of subcutaneous port access, e.g. reliable performance and low failure rates, high blood and fluid flows through the port with minimum degradation of the blood or other fluid, compatibility with peritoneal dialysis and other non-blood procedures and the ability to utilize an internal valve to provide improved isolation of the blood vessel or other accessed body lumen. Moreover, it would be desirable to overcome certain disadvantages associated with the buttonhole technique when used to access an A-V fistula. For example, it would be desirable if the tissue tract could be formed and accessed by different users so that the procedure could be employed in clinics and other locations where different personnel will treat different patients. Additionally, it would be desirable to reduce the formation of clot from back bleeding into the buttonhole tissue tract and thus lessen the need to remove the clot and reduce the risk of clot emboli. At least some of these objectives will be met by the invention described hereinafter.
2. Description of the Background Art
The "button hole" technique was first described by Dr. Zbylut Twardowski as the "constant site" access method in Twardowski et al. (1977) Pol. Arch. Med. Wewn. 57:205-214 and has been subsequently described in Scribner (1982) Proc. Europ. Dial. Transplant Assoc. 19:95-98 and Scribner (1984) Dial. Transplant 13:652. U.S. Pat. No. 5,562,617 and WO 95/19200, assigned to the assignee of the present application, describe implantable vascular access systems comprising an access port having an internal slit or duck bill valve for preventing back flow into the port. Vascular access ports having various articulating valves for isolating the port from the vascular system in the absence of external percutaneous connection to the port are described in the following U.S. Patents which name William Ensminger as an inventor: U.S. Pat. Nos. 5,527,278; 5,527,277; 5,520,643; 5,503,630; 5,476,451; 5,417,656; 5,350,360; 5,281,199; 5,263,930; 5,226,879; 5,180,365; 5,057,084; and 5,053,013. Other patents and published applications which show implantable ports having valve structures opened by insertion of a needle include U.S. Pat. Nos. 5,741,228; 5,702,363; 4,569,675; 4,534,759; 4,181,132; WO 97/47338; and WO 96/31246. Other patents and published applications relating to peritoneal dialysis include 5,770,417; 5,770,193; 5,752,939; and WO 98/17333. Implantable ports and subcutaneous catheters for connecting the ports for hemodialysis, peritoneal dialysis, and other procedures which are useful in the present invention are described in co-pending application Ser. Nos. 08/539,105; 08/724,948; 09/009,758; 08/942,990; 08/857,386; 08/896,791; 08/856,641; and 09/003,772, the full disclosures of which are incorporated herein by reference.